This invention relates to a system of butt-joining a flexible, belt-shaped material such as paper, plastic film or metal foil (which will be referred to as "web" hereinafter). More particularly it relates to a web butt-joining system in which electrical control is employed to butt-join webs, which are being run at high speed and with high accuracy.
Heretofore, in the case where a part of a web being fed out of a roll having the web wound on its core (the web being referred to as "an old web" hereinafter) is joined to the end of another web which will be newly fed (hereinafter referred to as "a new web"), the end portions of these new and old webs are overlaid, on one another. This method has been extensively employed. In this situation, the joined portion of the two webs is undoubtedly thicker than the remainder of the web. Therefore, when the web thus joined, for instance passes through a coating device or a printing machine, troubles due to the variation in thickness of the webs are caused in printing, coating or conveying the webs.
In order to eliminate this drawback, various techniques of butt-joining the ends of the new and old webs have been proposed. A device for practicing this method, is disclosed in U.S. Pat. Nos. 2,745,464; 3,654,035 and 3,717,057 or U.S. Pat. No. 3,939,031. Generally, such as device comprises a pair of rotatable drums for cutting the new and old webs, and a pair of or a single rotatable drum for sticking a bonding tape to the end portions of the two webs. A guide device guides the webs cut from the cutting position to the joining position. After being cut, the webs are conveyed to the joining position, and the webs are joined together with the bonding tape while being kept in an abutting relationship as the joining drum is rotated.
In general, in the web butt-joining device of this type, the cutting drums or the joining drums are driven in accordance with a mechanical driving system in which the driving power is transmitted through a clutch from the web feeding roll or its driving shaft or an electrical driving system in which DC motors coupled to the drums are employed. In the latter case, the clutch of the DC motors are operated in response to a detection signal provided when the end of the old web is detected.
In the device according to the former system, the cutting position is shifted by fluctuation of the operation of the clutch and the drum stop position is also shifted by fluctuation of the brake operation, with the lapse of time. Furthermore, the web running speed becomes different from the cutting drum circumferential speed because of the inertia of the web butt-joining device. Therefore, while the drums are being accelerated, the speed of the web feeding roll is varied. Accordingly, it is difficult to improve the web joining accuracy.
In the web butt-joining device according to the latter system, the DC motor is quickly accelerated according to the detection signal obtained when the end of the web is detected, thereby to provide speed synchronization. Since the speed synchronization is effected by speed control only, it is difficult to stop the cutting drums and the joining drums at their predetermined positions. The web is brought into contact with the drums whereby the web tends to be scratched, and speed synchronization cannot be completely obtained because the following start position is changed. If the speed synchronization is incomplete as described above, troubles such as low joining accuracy and web damage result. The degree of such difficulty is increased as the web running speed increases.
Accordingly, with the conventional device, it is difficult to cut and join the webs with high accuracy while the webs are being run at high speed, and accordingly it is necessary to decrease the speed of the entire production line or to decrease the speed of the line temporarily when the webs are joined together. This decrease of production line speed is opposite to the present tendency of increasing line speed based on remarkable technical progress in subsequent process steps.
The decrease of line speed may be prevented to an extent by providing a temporary web storing place such as a reservoir. However, as the processing speed in the subsequent processing is increased, more space is required for the temporary web storing, which results in an increase in manufacturing cost.